If you intend to make them persist automatically, then enable the service to start in the standard manner,
but ensure that the losetup is run early in the boot process, or instead, use an implicitly persistent
block device/partition.

Integration with tgtd

In RHEL based systems the config files in /etc/tgt/conf.d/ don't honor globbing.
Only the main /etc/tgt/targets.conf seems does.
So to avoid that issue causing tgtd to not start: